Various types of respirators are commonly worn by people who work in areas where the air may be contaminated with toxic or noxious substances such as airborne particulates, gases, and vapors. The type of respirator used in a particular environment depends on the amount and type of protection required by the wearer.
One general category of respirators typically includes those having a breathing mask with at least one filtered air inlet and at least one exhalation outlet or port. These respirators may be of the type referred to as half facepiece respirators, which typically cover the mouth and nose of the wearer, or of the type referred to as full facepiece respirators, which additionally cover the face and eyes of the wearer. With these types of respirators, the wearer pulls air through the filtered air inlet or inlets by drawing a breath, thereby creating a negative pressure in the mask. When the wearer exhales, the air released from the wearer's mouth creates a positive pressure in the mask, causing the air to exit the mask through the exhalation outlet or port when the positive air pressure reaches a certain level.
Another general type of respirator is referred to as a filtering facemask, which generally includes a mask body made of a filtering material that is permeable to air. The facemask may additionally include at least one exhalation outlet or port. This type of respirator typically covers the mouth and nose areas of the wearer. When in use, the wearer inhales and pulls air through the permeable mask material, then exhales and pushes air out of the facemask through the exhalation valve or port.
The components used for a particular respirator should not make breathing difficult for the wearer and ideally should allow the wearer to inhale and exhale comfortably when using the respirator. Respirator components that can affect the comfort of the respirator wearer are the valves, which may include both exhalation and inhalation valves. An exhalation valve selected for a respirator should allow a high percentage of air to easily escape from the interior portion of the breathing mask when the wearer exhales so that air pressure does not build up inside the mask. This can be accomplished by providing a valve portion that is displaced relatively easily from its valve seat when the wearer exhales. However, the valve portion also should seal easily against the valve seat when the wearer is not exhaling so that contaminated or unfiltered air does not unintentionally leak into the wearer's breathing zone. Although an inhalation valve would similarly allow for passage of air through the valve, it would typically be positioned in the opposite orientation from an exhalation valve. In this way, a valve portion would be displaced from its valve seat when the wearer inhales. It is also desirable that any valves provide the same protection to the wearer regardless of the orientation of the respirator.